The same as Ian H, I used Trainline.eu to book an InterCité, two overnight couchette trains and a TGV, all with bike reservations, back in the summer. No problems at all with presenting the tickets either on the SNCF phone app or as a pdf on the phone - after all, all they're after is the bar code. I also had print outs of the pdf files, just in case, but didn't need them. I could have saved all that extra weight!! ;-)